In co-pending U.S. patent application Ser. No. 419,705 filed on Sept. 20, 1982, a technique was disclosed that enables an optical designer to select compatible optical materials for the refractive elements of an optical system that is to be color-corrected at a specified number of wavelengths. A technique disclosed in co-pending U.S. patent application Ser. No. 260,106 filed on Oct. 20, 1988 enables the designer of a lens system that is to be color-corrected at a specified number of wavelengths to include one or more liquid lens elements among the lens elements of the system.
In co-pending U.S. patent application Ser. No. 282,665 filed on Dec. 12, 1988, examples were disclosed of apochromatic lens triplets of a type in which a liquid lens element is contained between two geometrically identical glass lens elements facing in opposite directions. In co-pending U.S. patent application Ser. No. 345,793 filed on May 1, 1989, examples were disclosed of apochromatic lens systems of a type in which a number of identical glass lens elements and a liquid lens element are used to achieve high performance as indicated by a change in focus of less than one-quarter wavelength over the visible spectrum.
Plastic lens elements are generally much lighter than glass lens elements of similar dimensions. Consequently, plastic lens elements are decidedly preferable to glass lens elements in applications requiring low weight (e.g., space-based optical systems). Furthermore, there are advantages with respect to manufacturing operations in using plastic lens elements due to the fact that plastic lens elements can be made by injection molding without requiring optical grinding and polishing. Techniques for producing plastic lens elements by injection molding to meet specified optical prescriptions are well known.